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For decades, most studies of ovarian aging have focused on its functional units, known as follicles, which include oocytes and granulosa cells. However, in the ovarian stroma, there are a variety of somatic components that bridge the gap between general aging and ovarian senescence. Physiologically, general cell types, microvascular structures, extracellular matrix, and intercellular molecules affect folliculogenesis and corpus luteum physiology alongside the ovarian cycle. As a result of damage caused by age-related metabolite accumulation and external insults, the microenvironment of stromal cells is progressively remodeled, thus inevitably perturbing ovarian physiology. With the established platforms for follicle cryopreservation and in vitro maturation and the development of organoid research, it is desirable to develop strategies to improve the microenvironment of the follicle by targeting the perifollicular environment. In this review, we summarize the role of stromal components in ovarian aging, describing their age-related alterations and associated effects. Moreover, we list some potential techniques that may mitigate ovarian aging based on their effect on the stromal microenvironment., (© 2023. The Author(s).)

Our previous study demonstrated that ovarian wild-type P53-induced phosphatase 1 (WIP1) expression decreased with age. We hypothesized that WIP1 activity was related to ovarian aging. The role of WIP1 in regulating ovarian aging and its mechanisms remain to be elucidated. Adult female mice with or without WIP1 inhibitor (GSK2830371) treatment were divided into three groups (Veh, GSK-7.5, GSK-15) to evaluate the effect of WIP1 on ovarian endocrine and reproductive function and the ovarian reserve. In vitro follicle culture and primary granulosa cell culture were applied to explore the mechanisms of WIP1 in regulating follicular development. This study revealed that WIP1 expression in atretic follicle granulosa cells is significantly lower than that in healthy follicles. Inhibiting WIP1 phosphatase activity in mice induced irregular estrous cycles, caused fertility declines, and decreased the ovarian reserve through triggering excessive follicular atresia and primordial follicle activation. Primordial follicle depletion was accelerated via PI3K-AKT-rpS6 signaling pathway activation. In vitro follicle culture experiments revealed that inhibiting WIP1 activity impaired follicular development and oocyte quality. In vitro granulosa cell experiments further indicated that downregulating WIP1 expression promoted granulosa cell death via WIP1-p53-BAX signaling pathway-mediated apoptosis. These findings suggest that appropriate WIP1 expression is essential for healthy follicular development, and decreased WIP1 expression accelerates ovarian aging by promoting follicular atresia and primordial follicle activation.

Research Question: What role does wild-type p53-induced phosphatase 1 (WIP1) play in the regulation of primordial follicle development?, Design: WIP1 expression was detected in the ovaries of mice of different ages by western blotting and immunohistochemical staining. Three-day-old neonatal mouse ovaries were cultured in vitro with or without the WIP1 inhibitor GSK2830371 (10 μM) for 4 days. Ovarian morphology, follicle growth and follicle classification were analysed and the PI3K-AKT-mTOR signal pathway and the WIP1-p53-related mitochondrial apoptosis pathway evaluated., Results: WIP1 expression was downregulated with age. Primordial follicles were significantly decreased in the GSK2830371-treated group, without a significant increase in growing follicles. The ratio of growing follicles to primordial follicles was not significantly different between the control and GSK2830371 groups, and no significant variation was observed in the PI3K-AKT-mTOR signal pathway. The inhibition of WIP1 phosphatase accelerated primordial follicle atresia by activating the p53-BAX-caspase-3 pathway., Conclusions: These findings reveal that WIP1 participates in regulating primordial follicle development and that inhibiting WIP1 phosphatase leads to massive primordial follicle loss via interaction with the p53-BAX-caspase-3 pathway. This might also provide valuable information for understanding decreased ovarian reserve during ovarian ageing., (Copyright © 2021 Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved.)

As a fundamental aging mechanism, cellular senescence causes chronic inflammation via the senescence-associated secretory phenotype (SASP). Theca-interstitial cells are an essential but little-studied component of follicle development in the ovarian microenvironment. In the present study, we observed significant cellular senescence in theca-interstitial cells and secretion of chemokine (C-C motif) ligand 5 (CCL5) by these cells during aging. Furthermore, we aimed to investigate whether and how senescence-associated secretory phenotype (SASP)-associated CCL5 may be involved in follicle development. Increased levels of CCL5 in the microenvironment of follicles attenuated preantral follicle growth, survival, and estradiol secretion. Oocyte maturation and the expression of zona pellucida 3 and differentiation factor 9 (GDF9) were also inhibited by CCL5. Granulosa cell apoptosis in follicles was promoted by CCL5, accompanied by the phosphorylation of nuclear factor-κB by CCL5 and inhibition of the PI3K/AKT pathway. These results suggest that SASP-associated CCL5 produced by senescent theca-interstitial cells may impair follicle development and maturation during ovarian aging by promoting granulosa cell apoptosis., (© 2019 Wiley Periodicals, Inc.)

There are about 1-2 million follicles presented in the ovary at birth, while only around 1000 primordial follicles are left at menopause. The ovarian function also decreases in parallel with aging. Folliculogenesis is vital for ovarian function, no matter the synthesis of female hormones or ovulation, yet the mechanisms for its changing with increasing age are not fully understood. Early follicle growth up to the large preantral stage is independent of gonadotropins in rodents and relies on intraovarian factors. To further understand the age-related molecular changes in the process of folliculogenesis, we performed microarray gene expression profile analysis using total RNA extracted from young (9 weeks old) and old (32 weeks old) mouse ovarian secondary follicles. The results of our current microarray study revealed that there were 371 (≥2-fold, q-value ≤0.05) genes differentially expressed in which 174 genes were upregulated and 197 genes were downregulated in old mouse ovarian secondary follicles compared to young mouse ovarian secondary follicles. The gene ontology and KEGG pathway analysis of differentially expressed genes uncovered critical biological functions such as immune system process, aging, transcription, DNA replication, DNA repair, protein stabilization, and apoptotic process were affected in the process of aging. The considerable changes in gene expression profile may have an adverse influence on follicle quality and folliculogenesis. Our study provided information on the processes that may contribute to age-related decline in ovarian function.

Mammalian oocytes go through a long and complex developmental process, while acquiring the competencies that are required for fertilization and embryogenesis. Recent studies revealed that the communication between oocytes and granulosa cells (GCs) is a critical process for female follicle development. In the current study, we aimed to study whether and how semaphorin 6C (Sema6c) regulated the cell junctions between oocytes and GCs in mice preantral follicles. The attenuation of SEMA6C expression by siRNA decreased the cell-cell junctions and accelerated follicle atresia in vitro. PI3K-AKT pathway was activated when SEMA6C expression was downregulated. And the LY294002, a PI3K inhibitor, could reverse the effect of low SEMA6C expression on cell junctions in preantral follicles. Our findings revealed that Sema6c was involved in follicle development, and the suppression of SEMA6C led to cell junction defection by activating the PI3K/AKT pathway, which might also provide valuable information for understanding premature ovarian failure and ovarian aging., (© 2018 Wiley Periodicals, Inc.)

The primordial follicle assembly, activation and the subsequent development are critical processes for female reproduction. A limited number of primordial follicles are activated to enter the growing follicle pool each wave, and the primordial follicle pool progressively diminishes over a woman's life-time. The number of remaining primordial follicles represents the ovarian reserve. Identification and functional investigation of the factors involved in follicular initial recruitment will be of great significance to the understanding of the female reproduction process and ovarian ageing. In this study, we aimed to study whether and how semaphorin 6C (Sema6c) regulated the primordial follicle activation in the neonatal mouse ovary. The attenuation of SEMA6C expression by SiRNA accelerated the primordial follicle activation in the in vitro ovary culture system. PI3K-AKT-rpS6 pathway was activated when SEMA6C expression was down-regulated. And the LY294002 could reverse the effect of low SEMA6C expression on primordial follicle activation. Our findings revealed that Sema6c was involved in the activation of primordial follicles, and the down-regulation of SEMA6C led to massive primordial follicle activation by interacting with the PI3K-AKT-rpS6 pathway, which might also provide valuable information for understanding premature ovarian failure and ovarian ageing., (© 2017 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.)

The initiation of primordial follicle development is essential for female fertility, but the signals that trigger this process are poorly understood. Given the potentially important roles of microRNAs (miRNAs) in the ovary, we aimed to study the expression patterns and regulatory functions of miRNAs during the initiation of primordial follicle development. Expression patterns of miRNA in the neonatal mouse ovary were profiled by microarray, and 24 miRNAs whose abundances differed significantly between ovaries from 3- and 5-day-old mice were identified. Pathway enrichment analysis revealed that 48 signal transduction pathways are modulated by the up-regulated miRNAs and 29 pathways are modulated by the down-regulated miRNAs (P-value and false discovery rate < 0.001). A miRNA-mRNA regulatory network was established for TGF-beta signaling pathway-related genes. Among the miRNAs involved in this pathway, miR-145 was chosen for further analysis. Down-regulation of miR-145 using an antagomir (AT) decreased the proportion and number of the primordial follicles and increased that of the growing follicles in the cultured ovaries (P < 0.05). The mean oocyte diameter in the primordial follicles was significantly greater in the AT group relative to the AT-negative control group (P < 0.05), whereas the mean oocyte diameter in growing follicles was smaller in the AT group than in the AT-negative control group. In addition, we confirmed that miR-145 targets Tgfbr2. The miR-145 AT caused an increase in TGFBR2 expression and activation of Smad signaling but did not affect the p38 MAPK or JNK pathway. These data suggest that miRNAs and the signaling pathways they modulate are involved in the initiation of primordial follicle development, and miR-145 targets Tgfbr2 to regulate the initiation of primordial follicle development and maintain primordial follicle quiescence.

Objective: To demonstrate the changes of ovarian aging markers across the Stages of Reproductive Aging Workshop (STRAW) stages and modify it with subclassification of mid reproductive age stage (MR)., Design: Healthy females were classified according to the STRAW system. Serum basal FSH, LH, E2, and anti-Müllerian hormone (AMH) were detected, FSH/LH ratio calculated, and antral follicle counts (AFCs) determined in follicular phase., Results: Progression through the whole STRAW stages under MR stage subdivided is associated with elevations in FSH, LH, FSH/LH ratio and decreases in E2, AMH and AFCs (p < 0.001). Both serum AMH and AFCs decreased early (after 25 years) and significantly (p < 0.01) with chronological age in MR stage. 0.982 ng/ml AMH and 3 antral follicles (low level of MR 25-30 years) were set as cutoffs to distinguish MR stage into early mid reproductive age (EMR) and late mid reproductive age (LMR) stages. The women in EMR stage compared with LMR could retrieve more oocytes in IVF treatment (p < 0.05) and has a higher pregnancy chance (57.9%) though not significant., Conclusion(s): The early and marked fall in serum AMH levels and AFCs suggest fine markers to further categorize and define the MR stage, demonstrating disparate reproductive aging period with reduced ovarian reserve in young age across the STRAW stages.

Peroxiredoxin 2 (PRDX2) has been known to act as an antioxidant enzyme whose main function is H(2)O(2) reduction in cells. We aimed to study the expression patterns of PRDX2 in mouse ovaries and explore the function of this protein in apoptosis of granulosa cells (GCs). We found that the expression of the PRDX2 protein in atretic follicle GCs was markedly higher than in healthy follicle GCs. In vitro, the transfection of siRNA targeting the Prdx2 gene inhibited the proliferation and induced the apoptosis of primary cultured GCs. Furthermore, suppression of PRDX2 resulted in the augmentation of endogenous H(2)O(2), and the ability to eliminate the exogenous H(2)O(2) was attenuated. The expression of PRDX2 and nuclear factor kappa-light-chain-enhancer of activated B cells (NFKB), whose activity was inhibited by binding to IKB, increased in GCs treated with various concentrations of H(2)O(2) for 30 min. However, no significant change in cytoplasmic IKB expression was observed. At 2 h after treatment with H(2)O(2), nuclear NFKB expression level was reduced, cytoplasmic IKB expression was increased, and PRDX2 expression was unchanged. Silencing of the Prdx2 gene caused early changes in NFKB and IKB expression in the primary cultured GCs compared to that in control cells. Taken together, these data suggest that PRDX2 plays an important role in inhibiting apoptosis in GCs and that PRDX2 actions may be related to the expression of NFKB and IKB.

Theca-interstitial cells (TICs) and granulosa cells (GCs) are important components of follicles that support follicle development and hormone secretion, and are considered to be important cell models for basic research. However, no method currently exists for simultaneously isolating TICs and GCs from a single ovary of the immature mouse. Here, we sought to develop such a protocol using mechanical dissection combined with brief collagenase-DNase digestion. Morphological characteristics and molecular markers were detected to identify TICs and GCs. In isolated TICs, cholesterol side chain cleavage cytochrome P450 (P450scc) was expressed abundantly, but anti-Mullerian hormone (AMH) was expressed only at very low levels. This expression profile was reversed in GCs. In addition, TICs secreted large amounts of testosterone (T) and minimal amounts of estradiol (E2), while the converse was found in GCs. T concentrations rose gradually in TIC culture media as the concentration of added luteinizing hormone (LH) was increased. In GCs, E2 secretion increased as the follicle-stimulating hormone (FSH) concentration increased. Thus, mechanical dissection combined with collagenase-DNase digestion is a simple, effective and reproducible method for obtaining large numbers of highly purified and hormonally stimulated TICs and GCs from one ovary. [ABSTRACT FROM AUTHOR]